When driving my 2006 Ford Tauras, the RPM will increase 200 to 500 RPM, the car does not accelerate, feels sluggish and then within seconds returns to normal operation. This happens only once in a while and there are no problems with shifting as I accelerate from a stop.
It sounds like you are describing classic transmission slippage problems.
Have you checked the level, color and odor of the trans fluid?
If not, do that and then report your findings to us in this same thread.
Good thought. I will do that when the sun comes up and report back tomorrow.